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Installation practice for roof insulation

In roof structures, too, thermal bridges must be eliminated as far as possible. In the roof insulation these can arise at eave and bargeboard junctions, at the intersection of gable and interior walls, chimneys and other structures on the roof.

Diagram of a roof, showing different edges (coloured lines) and types of dormers (numbered 1–16) (source: Roland Bergmann Dipl.Ing.(FH) Architekt; https://de.wikipedia.org/wiki/Ortgang#/media/File:Dachgauben_Dachkanten_de_Text.png, adapted)

Point thermal bridges can also occur, for example with satellite dish mountings, which interfere with the continuous insulation layer.

In between-rafter insulation, thermal bridges are caused by the rafters within the insulation layer, which must be taken into account for calculating the U value. In below-rafter insulation, thermal bridges can occur where walls extend to the rafters and thus into the insulation layer. Over-rafter insulation causes fewer problems with thermal bridges.

The airtight level is always implemented on the warm side, i.e. the inside of the insulation. For over-rafter insulation this is easy; but for between-rafter insulation, which is installed from above, it is more difficult, because a foil is laid over and between the rafters, and there is a risk of condensation there. In below-rafter insulation, walls which reach the rafters may possibly inter-fere with the airtight level.

If the roof structure is made impermeable to diffusion, a complete air seal is vital for the structure to function properly.

If the roof is renovated on its own to start with, the details of transitions and junctions should still be prepared properly with a view to future renovation measures. For example, sufficient roof overhang beyond the exterior walls can be prepared at eaves and bargeboards, where the external wall insulation can later join on. From a design perspective, care should be taken at this point that the final result be harmonious in detail. Thermal bridges at these transitions must of course be thought over in advance.